This proposal is designed to define the hormonal (vasopressin, cAMP, prostaglandin, and aldosterone) and volume factors which may regulate the activation of the components of the kallikrein-kinin system. It is also designed to examine the physiological role of this system in the regulation of sodium and water excretion by the kidney. By using specific blockers and potentiators of the endogenous kallikrein-kinin system, we will study this system's direct effect on the transport of sodium and water across epithelial membranes (toad urinary bladder) and its effect on the regulation of sodium and water excretion in the intact kidney.